Various conventional train protection systems have been developed around the globe with the goal to provide railway technical installations to ensure safe operation in the event of human failure.
Positive Train Control (PTC) refers to conventionally known technology that is designed to prevent train-to-train collisions, overspeed derailments, casualties or injuries to roadway workers operating within their limits of authority as a result of unauthorized incursion by a train as well as prevent train movements through a switch left in the wrong position. Although PTC systems vary widely in complexity and sophistication based on the level of automation and functionality they implement, the system architecture utilized and the degree of train control they are capable of assuming, PTC systems are consistent in that they are processor-based signal and train control systems (see Title 49 Code of Federal Regulations (CFR) Part 236, Subpart H) that utilize both computers and radio data links to accomplish PTC functions, e.g., monitoring and controlling train movements to provide increased safety.
More specifically, PTC requires that a train receives information about its location and where it is allowed to safely travel, i.e., “movement authorities.” Equipment on board the train enforces these movement authorities thereby preventing unsafe movement. PTC systems often use Global Positioning System (GPS) navigation to track train movements or utilize other mechanism to calculate their track location. Thus, PTC is meant to provide train separation or collision avoidance, line speed enforcement, temporary speed restrictions and ensure rail worker wayside safety.
However, various other benefits may be achieved by use of PTC; for example, the information obtained and analyzed by PTC systems can enable on-board and off-board systems to control the train and constituent locomotives to increase fuel efficiency and to perform locomotive diagnostics for improved maintenance. Because the data utilized by the PTC system is transmitted wirelessly, other applications can use the data as well.
Early train protection systems were termed “train stops,” which are still used by various metropolitan subway systems. In such implementations, beside every signal is a moveable clamp, which touches a valve on a passing train if the signal is red and opens the brake line, thereby applying the train's emergency brake; if the signal shows green, the clamp is turned away and does not impede operation of the train.
Other systems include the Integra-Signum system, wherein trains are influenced only at given locations, for instance whenever a train ignores a red signal, the emergency brakes are applied and the locomotive's motors are shut down. Additionally, such systems often require the operator to confirm distant signals (e.g., Continuous Automatic Warning System-CAWS) that show stop or caution; failure of a train operator to respond to the signal results in the train stopping. Such an implementation provides sufficient braking distance for trains following each other; however, such confirmation based systems do not always prevent accidents in stations where trains cross paths, because the distance from the red signal to the next obstacle may be too short for the train to brake to a stop.
More advanced systems, e.g. PZB or Indusi provide intermittent cab signaling and a train protection system that calculate a braking curve that determines if the train can stop before the next red signal, and brakes the train if the train cannot do so. One disadvantage to this approach is that acceleration of the train is prevented before the signal if the signal has switched to green. To overcome that problem, some systems, such as the Linienzugbeeinflussung, allow additional magnets to be placed between distant and home signals, or data transfer from the signaling system to the onboard computer is continuous.
Newer conventional PTC train protection systems use cab signaling, wherein the trains constantly receive information regarding their relative positions to other trains. In such systems, on-train computer processors run software that shows the train operator how fast he may drive, instead of him relying on exterior signals. Systems of this kind are in common use for high speed trains, where the speed of the trains makes it difficult if not impossible for the train operator to read exterior signals, and lengths of trains or distances between distant and home signals are too short for the train to brake.